n=int(input())
C = list(input())
ans = 0
N = n-1
for l in range(n):
    if C[l] == "W":
        for r in range(N,0,-1):
            if r<=l:
                print(ans)
                exit()
            if C[r] == "R":
                #print(C)
                C[l] = "R"
                C[r] = "W"
                #print(C)
                #print("-----------------")
                ans += 1
                N = r-1
                break
print(ans) n=int(input()) n int(input()) int input() input C = list(input()) C list(input()) list input() input ans = 0 ans 0 N = n-1 N n-1 n 1 for l in range(n):
    if C[l] == "W":
        for r in range(N,0,-1):
            if r<=l:
                print(ans)
                exit()
            if C[r] == "R":
                #print(C)
                C[l] = "R"
                C[r] = "W"
                #print(C)
                #print("-----------------")
                ans += 1
                N = r-1
                break l range(n) range n if C[l] == "W":
        for r in range(N,0,-1):
            if r<=l:
                print(ans)
                exit()
            if C[r] == "R":
                #print(C)
                C[l] = "R"
                C[r] = "W"
                #print(C)
                #print("-----------------")
                ans += 1
                N = r-1
                break C[l] == "W" C[l] C l "W" for r in range(N,0,-1):
            if r<=l:
                print(ans)
                exit()
            if C[r] == "R":
                #print(C)
                C[l] = "R"
                C[r] = "W"
                #print(C)
                #print("-----------------")
                ans += 1
                N = r-1
                break r range(N,0,-1) range N 0 -1 if r<=l:
                print(ans)
                exit()
             r<=l r l print(ans) print ans exit() exit if C[r] == "R":
                #print(C)
                C[l] = "R"
                C[r] = "W"
                #print(C)
                #print("-----------------")
                ans += 1
                N = r-1
                break C[r] == "R" C[r] C r "R" C[l] = "R" C[l] C l "R" C[r] = "W" C[r] C r "W" ans += 1 ans 1 N = r-1 N r-1 r 1 break print(ans) print ans N = r-1 r-1 N N = n-1 n-1 N C = list(input()) list(input()) C n=int(input()) int(input()) n ans = 0 0 ans ans += 1 1 ans
n=int(input())
C = list(input())
ans = 0
N = n-1
for l in range(n):
    if C[l] == "W":
        for r in range(N,0,-1):
            if r<=l:
                print(ans)
                exit()
            if C[r] == "R":
                #print(C)
                C[l] = "R"
                C[r] = "W"
                #print(C)
                #print("-----------------")
                ans += 1
                N = r-1
                break
print(ans)